The ability to accurately and reliably determine the presence or otherwise of a particular compound on an everyday object is of significant importance to customs and police forces around the world. The compounds of highest interest include illicit drugs and explosives and it is their detection in both a forensic context and with regard to the detection of contraband or tariff evasion that is of interest to police and customs forces respectively. Generally, the compounds of interest are likely to be present only in extremely small, or trace, amounts. Consequently, extremely sensitive chemical analysis techniques are employed to determine the presence or otherwise of a particular compound (target compound analysis).
One such analytical approach known from the prior art is to use a tandem mass spectrometer to chemically analyse a collected sample. However, the prior art techniques for analysing collected samples, and more particularly in the preparation of the samples prior to analysis by the mass spectrometer, can be both complex and time consuming. For example, bank notes would be sampled by taking bundles of bank notes and shaking them over a sheet of aluminium foil. Any particles deposited on the foil would then be vacuumed up, the vacuum cleaner including a removable filter, and the filter on the vacuum cleaner would be sampled using the tandem mass spectrometer. To sample each filter would generally require extensive sample preparation and sometimes chemical treatment prior to analysis. This would include several handling steps that would usually involve the use of solvents and the glassware. As well as being time consuming, the extensive preparation of the filters introduces an increased possibility of contamination of the sample. In addition, the sampling of bundles of money is not ideal as illicit drugs, such as cocaine, is found on most bank notes in general circulation. To determine the pattern of contamination it is necessary to analyse individual bank notes. Such individual analysis requires a large volume of individual filters to be analysed and therefore is time consuming when using prior art analysis methods. Similar problems and disadvantages are experienced when using sample collectors other than filters, such as swabs (dressings).
In UK patent application GB 2363517 A the current applicants discuss the introduction of a sample to a mass spectrometer by heating a sheet-like carrier, such as a bank note, within a confined space between two heated bodies such that a sufficient quantity of substance is desorbed from the carrier to be passed directly into the ionisation chamber of a mass spectrometer for subsequent analysis. Whilst suitable for the rapid sampling of individual bank notes, or other thin card or paper items, the apparatus described in GB 2363517 A is not suitable for use with filters or other sample collectors, of the type referred to above. This is because the sampled particles contained in such sample collectors tend, in addition to collecting on the surface, to be embedded in the collector material, as opposed to simply being present on the surface of a bank note. It should also be understood that the filters are used to remotely collect samples (by adsorbtion) where it is not possible to directly desorb the artefact of interest, such as a banknote. Direct desorption of an artefact, such as a banknote, is the most desirable method because it is the most efficient. Most sample collectors (adsorbers) are at best only a few percent efficient. This being so, a very effective desorption method is necessary to transfer the collected material into the instrument ionization region. Also materials of interest are most efficiently desorbed from the filter when subjected to their optimum desorption temperature, this temperature varies according to the material of interest.
GB-A-2 262 203 discloses a desorbing unit for analysis of vapours and particles desorbed from a porous flexible sampling disc. The unit includes two metal blocks that define a cavity therebetween in which the sampling disc is placed. The blocks incorporate straight air passages that allow air to pass through the sampling disc under pressure. The blocks are maintained at a high temperature. U.S. Pat. No. 5,741,984 describes an apparatus for the collection of a chemical sample from the fingers of an individual for subsequently analysis comprising a token that is removed from a dispenser. A token handler for use in association with the token and an analyzer is also disclosed.